This invention relates to an electronic balance which has both a function of automatic sensitivity calibration and a function of automatic linearity calibration.
Generally, the electronic balances which have a function of automatic sensitivity calibration are provided with a built-in weight for sensitivity calibration and a mechanism for loading and unloading the weight on and from the load sensor of the balance, so that upon occurrence of a certain amount of change in the ambient temperature or lapse of a predetermined period of time, the calibration weight is automatically put on the load sensor, the output of which is compared with the mass of the calibration weight stored therein beforehand so as to change the sensitivity coefficient.
In such electronic balances as mentioned above, by providing a plurality of calibration weights and placing all of them simultaneously or each of them separately and successively on the load sensor, it is possible to perform both sensitivity and linearity calibrations simultaneously. The sensitivity calibration can be conducted on the basis of the output data of the load sensor obtained at zero point, that is, when no load is applied to the load sensor and the output data thereof obtained at a point of measurement near the maximum weight that can be measured by the balance, that is, when a weight of a known mass near the maximum measurable weight of the balance is applied thereto. For linearity calibration, however, it is necessary to have measurement data obtained at one more point between the above-mentioned two points. To this end, there may be provided two calibration weights, the total mass of which approximates the maximum measurable weight of the balance, so that by using the data obtained when both the weights are loaded on the balance and the data obtained when only one of them is loaded thereon it is possible to perform both sensitivity and linearity calibrations.
In conventional electronic balances having the above-mentioned functions, as previously mentioned, when a predetermined amount of change has occurred in the ambient temperature or a predetermined period of time has passed, a linearity calibration is always conducted along with sensitivity calibration.
Needless to say, it is desirable that the time required for such calibration should be as short as possible. In known balances capable of both sensitivity and linearity calibration it is necessary to load and unload a plurality of built-in weights on and from the load sensor, so that a long period of time is required for the operation of calibration.
Accordingly, the primary object of the invention is to make shorter than otherwise the time required for the operation of calibration in an electronic balance capable of sensitivity and linearity calibration.